Hierarchical encoding is widely supported in current broadcast standards. In broadcast systems, the capacity is typically limited by the worst user in the coverage area. By using hierarchical encoding, users with a limited signal to noise ratio (SNR) may only receive low quality video. Users with high SNR may take advantage of hierarchical encoding to receive high quality. Therefore, overall MBS capacity is improved.
Current techniques supporting hierarchical encoding by layered modulation is limited in single input single output (SISO) transmissions. For example, the 16QAM constellation used in DVB-T has 3 formats, one non-layered constellation, and two layered constellations for hierarchical encoding as shown in FIG. 1 at 100 and FIG. 2 at 200. FIG. 1 depicts a first 110 layered 16QAM modulation format in DVB-T and FIG. 2 depicts a second 210 layered 16QAM modulation format in DVB-T; A similar layered constellation is also defined in the MediaFLO standard, where only the scale of the constellation is changed slightly. The layered constellation provides an essential improvement for broadcast services. The limitations are (1) only two level of adaptation is available as defined in both DVB-T and MediaFLO; and (2) it can only be used in single transmit antenna case.
Thus, a strong need exists for improved techniques for hierarchical encoding for multicast broadcast services in wireless communication systems.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.